Many scientists contend that release of refrigerants into the atmosphere deleteriously affects the ozone layer that surrounds and protects the earth from ultraviolet solar radiation. Recent international discussions and treaties, coupled with related regulations and legislation, have renewed interest in devices for recovery and storage of used refrigerants from refrigeration equipment for later purification and reuse, or for proper disposal. U.S. Pat. No. 4,261,178, assigned to the assignee hereof, discloses a refrigerant recovery system in which the inlet of a compressor is coupled through an evaporator and through a manual valve to the refrigeration equipment from which refrigerant is to be recovered. The compressor outlet is connected through a condenser to a refrigerant storage container. The condenser and evaporator are combined in a single assembly through which cooling air is circulated by a fan. Content of the storage container is monitored by a scale upon which the container is mounted for sensing weight of liquid refrigerant in the container, and by a pressure switch coupled to a the fluid conduit between the condenser and the container for sensing vapor pressure within the storage container. A full-container condition sensed at the scale or a high-pressure condition sensed at the pressure switch terminates operation of the compressor motor. A vacuum switch is positioned between the inlet valve and the evaporator for sensing evacuation of refrigerant from the refrigeration equipment and automatically terminating operation of the compressor motor.
U.S. Pat. No. 4,768,347, also signed to the assignee hereof, discloses a refrigerant recovery system that includes a compressor having an inlet coupled through an evaporator and through a solenoid valve to the refrigeration equipment from which refrigerant is to be withdrawn, and an outlet coupled through a condenser to a refrigerant storage container or tank. The refrigerant storage container is carried by a scale having a limit switch coupled to control electronics to prevent or terminate further refrigerant recovery when the container is full. The scale comprises a platform pivotally mounted by a hinge pin to a wheeled cart, which also carries the evaporator/condenser unit, compressor, control electronics, and associated valve and hoses.
Although the systems disclosed in the noted patents address and overcome problems theretofore extant in the art, further improvements remain desirable. For example, a problem remains relative to recovering refrigerant from large commercial chiller systems and the like that employ low-pressure refrigerants such as R11 and R123. The boiling point of trichloro-monofluoromethane (R11) is 74.9.degree. F., and the boiling point of dichloro-trifluoroethane (R123) is 82.2.degree. F. In order to function at normal evaporation temperatures in the 40.degree. to 50.degree. F. range, each of these refrigerants must operate at a considerable vacuum. A recovery system for low-pressure refrigerant of this character would require an significant amount of auxiliary heat in an evaporator if the refrigerant were pumped during recovery only in vapor phase, requiring excessive energy and long recovery times.
Copending parent application Ser. No. 07/799,433 discloses a refrigerant recovery system that includes a refrigerant accumulator having an inlet port for connection to the liquid port of equipment from which refrigerant is to be recovered, a vapor outlet port connected to the inlet of a refrigerant compressor, and a liquid outlet port. The liquid outlet port of the accumulator is connected to the inlet of a liquid refrigerant pump, which has an outlet for connection to a refrigerant storage container. A liquid refrigerant sensor is coupled to the accumulator and responsive to presence of liquid refrigerant within the accumulator. Valves are coupled to the compressor outlet and responsive to presence of liquid within the accumulator for connecting the compressor outlet either to the vapor port of the equipment from which refrigerant is to be recovered for pressurizing the refrigerant and enhancing flow of refrigerant to the accumulator, or through a fan-cooled condenser to the refrigerant storage container.
The liquid refrigerant pump in the system disclosed in the parent application is a magnetically coupled pump that is capable of pumping liquid refrigerant from the accumulator to the storage container against a limited head, typically between 30 and 60 psi depending upon the type of pump. This would not typically be a problem for low-pressure refrigerants such as R11 and R123, but would be a problem for high-pressure refrigerants such as R12, R22 and R502. However, the compressor may so reduce pressure within the vapor space of the accumulator that the pressure differential experienced by the liquid pump will decouple the pump. It is therefore a general object of the present invention to provide a system for recovering low-pressure and high-pressure refrigerants in which the refrigerant is recovered primarily in liquid phase, and in which the liquid pump is protected against excess pressure differential across the pump. Another and more specific object of the present invention is to provide a refrigerant recovery system of the described character that is adapted to control pressure differential across the liquid pump in association with differing refrigerants and/or varying ambient temperatures.